We consider a model for the cyclic brightness variations of a young star with a low-mass companion that accretes matter from the remnants of a protostellar cloud .
At small inclinations of the binary orbit to the line of sight , the streams of matter and the density waves excited in the circumbinary disk can screen the primary component of the binary from the observer .
To study these phenomena , we have computed grids of hydrodynamic models for binary systems by the SPH method based on which we have constructed the phase light curves as a function of the rotation angle of the apsidal line relative to the observer .
The model parameters were varied within the following ranges : the component mass ratio q = 0.01 - 0.1 and the eccentricity e = 0 - 0.5 .
We adopted optical grain characteristics typical of circumstellar dust .
Our computations have shown that the brightness oscillations with orbital phase can have a complex structure .
The amplitudes and shapes of the light curves depend strongly on the inclination of the binary orbit and its orientation relative to the observer and on the accretion rate .
The results of our computations are used to analyze the cyclic activity of UX Ori stars .

Key words : young binary systems , hydrodynamics , cyclic activity , accretion .